Maria Totsuka is a young human girl who attends Seiseki Girls' Academy, where she serves as a health committee member and is known for her quiet, gentle, and caring nature. Before her fateful encounter with the archangel Lucifer, she devoted herself to her friends and her religious faith. Maria possesses an unusual gift of sight that allows her to perceive celestial and demonic beings that are normally invisible to humans.

Her story begins when Lucifer, cast out of Heaven, crash-lands into the school’s church during her descent to Hell. Maria witnesses the event, and Lucifer secretly infuses a portion of her angelic blood into the girl’s body. After Lucifer is defeated by the Seven Sins and sealed with the cursed Garb of Punishment, she returns to Earth and rips out Maria’s heart, binding her as an immortal, eternally youthful servant. Though initially unwilling, Maria gradually becomes devoted to her new mistress.

Maria’s primary motivation shifts from her ordinary school life to serving Lucifer in her quest for revenge against the Seven Sins. Her role in the story is that of Lucifer’s human companion and ally, often assisting alongside the demon lord Leviathan. Her relationship with Lucifer evolves from forced servitude to a genuine, if complex, loyalty. She also interacts with the various Demon Lords and other characters encountered during their journey.

As a result of Lucifer’s blood and the removal of her heart, Maria gains immortality and eternal youth, and retains her ability to see supernatural beings. Additionally, the infusion of angelic blood grants her the power to locate and track those who have wronged Lucifer, enabling her to aid in exacting revenge. Over the course of the series, she develops from a passive, unwilling pawn into a more active participant in Lucifer’s schemes, while still retaining her core kindness and humanity.